Herbicidal compositions

ABSTRACT

PCT No. PCT/EP95/04752 Sec. 371 Date Aug. 22, 1997 Sec. 102(e) Date Aug. 22, 1997 PCT Filed Dec. 1, 1995 PCT Pub. No. WO96/17519 PCT Pub. Date Jun. 13, 1996The invention relates to compositions comprising: a) a 4-benzoylisoxazole of formula (I) wherein R, R1 and R2 are as defined in the description; and b) N-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4&#39;-fluoro-oxyacetanilide) having formula (II) and to their use as herbicides.

This application is a 371 of PCT/EP95/04752, filed Dec. 01, 1995.

TECHNICAL FIELD

This invention relates to new compositions comprising anN-isopropylheteroaryloxyacetanilide herbicide and a 4-benzoylisoxazolederivative, and to their use as herbicides.

BACKGROUND ART

The compounds of the invention are known in the art.N-Isopropylheteroaryloxyacetanilides are described in European PatentPublication Number 0348737, published on Jan. 3, 1990, which inparticular disclosesN-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-(4'-fluoro-oxyacetanitide)as compound 34. 4-Benzoylisoxazoles are described in for exampleEuropean Patent Publication Numbers 0418175, 0487357, 0527036 and0560482. In particular, European Patent Publication Number 0560482,published on Feb. 10, 1993, discloses5-cyclopropyl-4-(2-methylsulphonyl-4-trifluoromethylbenzoyl)isoxazole.Each of these publications teach that these compounds possess herbicidalactivity. However, neither of the publications teach specificanti-gramineous properties in the compounds. EP-A1-0348737 teaches thatthe acetanilide compounds may be applied at from 0.01 to 10 kg of activecompound per hectare of soil surface, preferably 0.05 to 5 kg per ha; nodetails of the precise dose rates used for the application of thecompounds to treat graminea EP-A1-0527036 teaches that the compounds ofthe invention possess high activity in comparison with known compoundsagainst certain weed species.

Hence the literature does not teach mixtures of these compounds; nordoes it suggest that such a mixture would be expected to be particularlyusefull as an anti-graminicide. At present the most commonly usedmixture in this area of weed science comprises metolachlor and atrazine.These are frequently recommended for use at dose rates from about 1 to2.5 kg/ha of metolachlor and from 0.5 to 2.5 kg/ha of atrazine. Anobject of the invention is thus to provide a mixture suitable as agraminicide which may be used at reduced dose rates of active compoundin comparison with the known products.

Remarkably, it has been found that the mixture ofN-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanihide)with 4-benzoylisoxazole derivatives provides effective control of anextremely wide range of both monocotyledon and dicotyledon weeds atreduced dose rates when compared with these known compounds. Moreover itprovides effective control together with selectivity in important cropspecies such as maize.

Surprisingly, and in addition to this, it has been found that in certainconditions the combined herbicidal activity of certain4-benzoylisoxazoles withN-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetaanilde)for the control of certain weed species e.g. Setaria viridis,Echinochloa crus-galli, Amaranthius retroflexus and Polygonumlapathifolium, is greater than expected, without an unacceptableincrease in crop phytotoxicity, i.e the mixture shows synergism asdefined by Limpel, L. E., P. H. Schuldt and D. Lamont, 1962, 1. Proc.NEWCC 16, 48-53, also known as the Colby formula (Colby S. R., 1967,Weeds 15, 20-22), using the formula: ##EQU1## where E=the expectedpercent inhibition of growth by a mixture of two herbicides A and B atdefined doses.

X=the percent inhibition of growth by herbicide A at a defined dose.

Y=the percent inhibition of growth by herbicide B at a defined dose.

When the observed percentage of inhibition by the mixture is greaterthan the expected value E using the formula above the combination issynergistic.

This remarkable synergistic effect gives improved reliability incontrolling these competitive weeds of many crop species, andcontributes to a considerable reduction in the amount of activeingredient required for weed control.

DISCLOSURE OF INVENTION

According to the present invention there is provided a method ofcontrolling the growth of weeds at a locus which comprises applying tosaid locus a herbicidally effective amount of:

(a) a 4-benzoylisoxazole of formula (I): ##STR2## wherein R is hydrogenor --CO₂ R³ ;

R¹ is cyclopropyl;

R² is selected from halogen, --S(O)_(p) Me and trifluoromethyl,

n is two or three; p is zero, one or two; and

R³ is C₁₋₄ alkyl; and

(b)N-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide)having the formula (II): ##STR3##

Preferably the 4-benzoylisoxazole derivative of formula (I) is5-cyclopropyl-4-(2-methylsulphonyl-4-trifluoromethyl)-benzoylisozaxole,hereafter referred to as Compound A. For convenienceN-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide)is hereafter referred to as compound B.

The amounts of the 4-benzoylisoxazole and compound B applied varydepending on the weeds present and their population, the compositionsused, the timing of the application, the climatic and edaphicconditions, and (when used to control the growth of weeds in cropgrowing areas) the crop to be treated. In general, taking these factorsinto account, application rates from 5 to 500 g of 4-benzoylisoxazoleand from 10 to 10,000 g of compound B per hectare give good results.However, it will be understood that higher or lower application ratesmay be used, depending upon the problem of weed control encountered.

The method of the invention is most preferably used for the control ofweeds at a locus used, or to be used for the growing of a crop. Whenapplied to a crop-growing area, the rate of application should besufficient to control the growth of weeds without causing substantialpermanent damage to the crop.

Crops which the mixture may be used with include soyabeans, sugarcane,cotton, maize, sunflower, peas, chickpeas, potatoes, sorghum rice andcereals. The preferred crop, in terms of the selectivity of the mixture,is maize. For the selective control of weeds at a locus of weedinfestation which is an area used, or to be used, for growing of cropsapplication, rates from about 5 to 200 g of 4-benzoylisoxazole and fromabout 50 to 5,000 g of compound B per hectare are particularly suitable,preferably from about 50 to 130 g of 4-benzoylisoxazole and from about80 to 875 g of compound B per hectare, most preferably from 75 to 100 g(about 80 g being most preferred) of 4-benzoylisoxazole and from 300 to500 g (about 360 g being most preferred under humid conditions and about450 g under more dry conditions) of compound B per hectare.

The mixture is preferably applied pre-emergence but can also be appliedpost-emergence (especially at an early stage of weed growth). By theterm `pre-emergence application` is meant application to the soil inwhich the weed seeds or seedlings are present before emergence of thecrop. One example of a pre-emergence application is known as `pre-plantincorporated` (PPI), where the herbicide is incorporated into the soilbefore planting the crop. Early PPI application may also be used. Themixture may also be applied pre-planting (i.e. before the crop isplanted) either to the surface of the soil or soil-incorporated. Earlypre-plant treatments using the mixture (particularly surface applied)are also a feature of the method of the invention.

According to a further feature of the present invention there areprovided herbicidal compositions comprising:

(a) a 4-benzoylisoxazole derivative of formula I as defined above; and

(b)N-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide);

in association with, and preferably homogeneously dispersed in, aherbicidally acceptable diluent or carrier and/or surface active agent.

The term "herbicidal composition" is used in a broad sense, to includenot only compositions which are ready for use as herbicides but alsoconcentrates which must be diluted before use. Preferably, thecompositions contain from 0.05 to 90% by weight of 4-benzoylisoxazoleand compound B.

Unless otherwise stated, the percentages and ratios appearing in thisspecification are by weight.

Generally a composition in which the ratio of (a):(b) is from about1:2000 to 50:1 to wt/wt is used, proportions from about 1:1000 to 4:1wt/wt being preferred, with proportions from about 1:17.5 to 1.63:1wt/wt being more preferred, and proportions from about 1:6.67 to 1:3wt/wt being especially preferred (ratios of about 1:4.5 in humidconditions and about 1:5.6 in dry conditions being most preferred).

The preferred formulation according to the invention is in the form of awater dispersible granule, although it will be understood that otherformulation types known in the art may also be used.

In accordance with the usual practice, a tank mix may be prepared priorto use by combining separate formulations of the individual herbicidalcomponents.

According to a further feature of the present invention, there isprovided a product comprising:

(a) 4-benzoylisozaxole of formula I as defined above; and

(b)N-isopropyl-(5-trifiuoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide),

as a combined preparation for simultaneous, separate or sequential usein controlling the growth of weeds at a locus.

The following non-limiting experiments illustrate the present invention.

Experiment A1

The following experiments were conducted on Compound A and Compound B invarious field research stations in Europe during May. Compound A (as a750 g/kg water dispersible granule formulation) and Compound B (as a 600g/kg water dispersible granule formulation) were tested at the followingdose rates (note that hereafter ai means active ingredient):

    ______________________________________    Compound A:        50, 75, 100, 125 g ai/ha    Compound B:        240, 366, 480, 600 g ai/ha    Compound A + Compound B:                       50 + 240/360/480 g ai/ha                       75 + 240/360/480 g ai/ha                       100 + 240/360/480 g ai/ha    ______________________________________

Trial and application conditions are given below in Table 1 (in theTables that follow DAT means days after treatment):

                  TABLE 1    ______________________________________               Chazay               D'azergues   Alzonne Bologna    LOCATION →               France       France  Italy    ______________________________________    Soil texture                    sandy loam    % Org. matter               1.8          1.4     1.82    pH         6.9          7.9     8.13    % Sand     38           34      34    % Silt     41           39      46    % Clay     17           22      29    Rainfall mm               25/19        37/55   24/146    15/30 DAT    Temperature               13° C.                            18° C.                                    19° C.    (when applied)    Soil       WET          DRY     DRY    ______________________________________

Weeds were drilled on the same day as maize. All trials were sprayedpre-emergence of the maize on the same day as drilling or within 2 daysafterwards. Soil conditions were warm and wet, so that the crop andweeds emerged and grew quickly. Rainfall or irrigation occurred within15 days of application. The results are expressed as a percentagephytotoxicity, as shown in Table 2 below. In this Table "Obs" is theobserved value the value in brackets (Exp) is the expected valuecalculated using the Colby formula.

Results:

                                      TABLE 2    __________________________________________________________________________          Echinochloa                 Echinochloa                       Setaria                              Amaranthus                                    Polygonum          crus-galli                 crus-galli                       viridis                              retroflexus                                    lapathifolium    Species          ALZONNE                 BOLOGNA                       BOLOGNA                              ALZONNE                                    CHAZAY    Dose rate          Obs (Exp)                 Obs (Exp)                       Obs (Exp)                              Obs (Exp)                                    Obs (Exp)    (g a.i./ha)          46DAT  54DAT 54DAT  46DAT 64DAT    __________________________________________________________________________    Cpd A     50    45     77    62     72    50     75    35     91    82     70    90    100    82     75    82     80    70    125    85    100    97     95    95    Cpd B    240    45     35    85     30    25    360    65     52    82     10    0    480    77     65    86     67    25    600    90     75    82     45    40    Cpd A + B     50 + 240           75 (70)                 100 (85)                       100 (94)                               95 (80)                                    100 (62)     75 + 240           90 (64)                 100 (99)                       100 (97)                               95 (79)                                     90 (92)    100 + 240           92 (90)                 100 (84)                       100 (97)                               84 (86)                                     90 (77)     50 + 360           87 (81)                 100 (89)                       100 (93)                              100 (75)                                     95 (50)     75 + 360          100 (77)                 100 (96)                       100 (97)                               92 (73)                                    100 (90)    100 + 360          100 (94)                 100 (88)                       100 (97)                               90 (82)                                    100 (70)     50 + 480           95 (87)                 100 (92)                       100 (95)                               87 (91)                                     65 (62)     75 + 480           85 (85)                 100 (97)                       100 (97)                               92 (90)                                    100 (92)    100 + 480          100 (96)                 100 (91)                       100 (97)                               85 (93)                                    100 (77)    __________________________________________________________________________

The Colby formula may be applied to the above data and indicates that in29 cases a better than expected level of weed control was observed (i.e.a synergistic interaction), in 2 cases a lower level of activity thanexpected was observed (i.e. antagonism) and in 14 cases the observedvalue was within 3% of the expected value (i.e. an additive effect).This clearly shows that in these trials the vast majority of the resultswere synergistic.

Experiment A2

The following experiments were conducted on the Compound A and CompoundB in various field research stations in the United States. Compound A(as a 750 g/kg water dispersible granule formulation) and Compound B (asa 600 g/kg water dispersible granule formulation) were tested at thefollowing dose rates:

    ______________________________________    Compound B + Compound A:                        240 + 75/100/125 g ai/ha                        360 + 75/100/125 g ai/ha                        480 + 75/100/125 g ai/ha    Compound A:         75/100/125/150 g ai/ha    Compound B:         240/360/480/600 g ai/ha    ______________________________________

A commercial standard was also applied comprising metolachlor andatrazine at 1120/1120 g ai/ha and 2240/2240 g ai/ha ofmetolachlor/atrazine. The trials were conducted in South Dakota (1trial), Nebraska (1), Iowa (1), Indiana (1), Pennsylvania (1) andMississippi (1). The weed species were seeds in all locations. Alltrials were sprayed in May/June on the same day or within 3 days ofmaize sowing. In all trials, significant rainfalls or irrigationoccurred shortly after spraying and for the next 2 or 3 weeks. The fieldtrial and application conditions were as shown in Table 3 below:

                                      TABLE 3    __________________________________________________________________________    LOCATION            S Dakota                 Nebraska                      Iowa Pennsylvania                                 Mississippi                                       Indiana    __________________________________________________________________________    Soil texture            silt loam                 silt loam                      silt loam                           loam  clay  silt loam    % Org. Matter            4.1  3.3  4    3     2.4   1.9    pH      6.1  6.4  7    6.9   6     6.2    % Sand  24   18   18   34    5.5   --    % Silt  52   58   56   44    38    --    % Clay  24   24   26   22    56    --    Rainfall mm            81/108                 19/49                      51/83                           62/28 78/15 27/146    15/30DAT    Soil temp. (appln)            18° C.                 26° C.                      25° C.                           20° C.                                 24° C.    SOIL (appln)            MOIST                 MOIST     DRY   DRY    __________________________________________________________________________

The mean results of the trials as a percentage of reduction in thegrowth of plant species at various stages after treatment are presentedin Tables 4 to 6 below. Note that in the Tables the weed species arerepresented by the following Bayer codes and that ATR means Atrazine andMET means metolachlor.

    ______________________________________    ABUTH =          Abutilon theophrasti    AMARE =          Amaranthus retroflexus    CHEAL =          Chenopodium album    DATST =          Datura stramonium    DIGSA =          Digitaria sanguinalis    ECHCG =          Echinochloa crus-galli    HELAN =          Helianthus annuus    IPOLA =          Ipomoea lacunosa    PANMI =          Panicum miliaceum    POLCO =          Polygonum convolvulus    SETFA =          Setaria faberi    SETLU =          Pennisetum glaucum    SETVI =          Setaria viridis    SORVU =          Sorghum vulgare    XANST =          Xanthium strumarium    ______________________________________

                                      TABLE 4    __________________________________________________________________________    Dose Rates (g a.i/ha)                 15DAT                     25DAT                          43DAT                              25DAT                                   43DAT                                        25DAT                                             43DAT 25DAT                                                       43DAT                                                           25DAT                                                               43DAT    Cpd A  Cpd B Maize                     Maize                          Maize                              ABUTH                                   ABUTH                                        AMARE                                             AMARE CHEAL                                                       CHEAL                                                           DATST                                                               DATST    __________________________________________________________________________    75      0    0   0    0   97   98   97   96    99  100 88  93    97.5    0    0   0    0   98   98   100  99    100 100 88  90    127.5   0    0   0    1   99   99   99   99    100 100 90  93    150     0    1   1    2   99   97   100  100   100 100 93  95    0      240   0   0    0   12   10   49   52    56  47  40  63    0      360   0   0    0   16   13   49   52    64  56  42  55    0      480   0   0    0   18   22   66   54    68  49  67  70    0      600   0   2    0   26   18   66   61    69  55  63  60    75     240   0   0    0   96   96   98   98    100 100 85  88    75     360   0   0    0   98   97   100  99    100 100 88  88    75     480   0   0    0   97   98   99   99    99  100 97  97    97.5   240   0   1    1   99   98   100  99    100 100 92  95    97.5   360   0   1    0   98   97   98   98    100 100 92  97    97.5   480   0   1    1   99   98   99   100   100 100 93  90    127.5  240   1   1    1   99   99   99   98    100 100 93  95    127.5  360   1   1    3   100  100  100  100   100 100 93  95    127.5  480   0   1    0   99   99   99   99    100 100 95  97    ATR + MET - 1120 + 1120                 0   0    0   63   50   99   99    98  100 92  97    ATR + MET - 2240 + 2240                 0   0    0   85   68   100  99    100 100 97  98    __________________________________________________________________________

                                      TABLE 5    __________________________________________________________________________    Dose Rates (g a.i/ha)                 25DAT                     25DAT                         43DAT                             25DAT                                 43DAT                                     25DAT                                         43DAT                                             25DAT                                                 43DAT                                                     25DAT                                                         43DAT    Cpd A  Cpd B DIGSA                     ECHCG                         ECHCG                             HELAN                                 HELAN                                     IPOLA                                         IPOLA                                             PANMI                                                 PANMI                                                     POLCO                                                         POLCO    __________________________________________________________________________    75      0    97  96  91  40  45  58  55  75  68   7  0    97.5    0    99  98  98  75  74  55  48  87  83   7  0    127.5   0    99  99  98  91  84  72  65  88  88   0  0    150     0    99  99  99  88  97  65  65  91  94  10  0    0      240   90  91  88   0   0  27  37  18  18   0  0    0      360   94  98  97   0   0  25  40  35  24   0  0    0      480   99  99  99   0   0  48  48  38  30   0  0    0      600   98  99  91   5   3  47  43  47  36   7  0    75     240   99  99  98  55  43  67  53  71  65   3  0    75     360   99  99  98  60  52  57  50  84  74  10  7    75     480   100 100 100 72  75  75  55  83  81   5  0    97.5   240   99  99  98  85  82  65  48  76  68   3  0    97.5   360   99  99  100 75  86  67  50  76  75  17  10    97.5   480   100 100 99  87  92  73  65  87  88   0  0    127.5  240   100 100 100 91  96  67  57  87  79  10  5    127.5  360   99  100 100 83  77  80  55  87  88  12  0    127.5  480   100 100 100 93  97  73  67  90  82  13  12    ATR + MET - 1120 + 1120                 99  99  98  96  99  78  72  56  43  97  97    ATR + MET - 2240 + 2240                 99  100 100 98  100 98  92  80  68  100 100    __________________________________________________________________________

                                      TABLE 6    __________________________________________________________________________    Dose Rates (g a.i/ha)                 25DAT                     43DAT                         25DAT                             43DAT                                 25DAT                                     43DAT                                         25DAT                                             43DAT                                                 25DAT                                                     43DAT    Cpd A  Cpd B SETFA                     SETFA                         SETLU                             SETLU                                 SETVI                                     SETVI                                         SORVU                                             SORVU                                                 XANST                                                     XANST    __________________________________________________________________________    75      0    97  94  89  77  92  86  88  78  52  49    97.5    0    98  96  90  83  96  92  85  83  60  65    127.5   0    99  98  96  91  95  95  90  92  70  68    150     0    99  98  98  93  97  97  90  90  73  80    0      240   88  85  73  59  80  76  22  22  13  13    0      360   93  84  79  56  92  84  43  30  13  16    0      480   95  59  88  75  92  90  60  55  16  11    0      600   96  94  89  85  95  94  72  40  17   8    75     240   97  94  95  89  95  92  77  75  50  25    75     360   99  98  97  97  97  96  88  83  50  38    75     480   98  98  97  95  97  97  82  78  49  38    97.5   240   98  97  93  92  96  94  82  78  61  50    97.5   360   98  97  96  94  96  95  82  73  55  49    97.5   480   100 99  98  97  99  99  87  83  64  58    127.5  240   99  98  98  95  97  96  83  70  63  58    127.5  360   100 100 99  99  99  98  87  82  72  73    127.5  480   99  99  98  98  98  97  87  72  74  73    ATR + MET - 1120 + 1120                 97  96  95  88  96  96  60  50  31  32    ATR + MET - 2240 + 2240                 99  99  98  96  98  98  73  52  65  76    __________________________________________________________________________

These results demonstrate that the mixture of 4-benzoylisoxazole andCompound B, when compared with the commercial standard atrazine andmetolachlor, remarkably provides a more effective level of weed controlagainst a number of weed species at substantially reduced applicationrates of active ingredient, as well as possessing selectivity againstthe crop species maize.

What is claimed is:
 1. A method of controlling the growth of weeds at alocus which comprises applying to said locus a synergistic herbicidallyeffective amount of:(a) a 4-benzoylisoxazole of formula (I): ##STR4##wherein R is hydrogen or --CO₂ R³ ;R¹ is cyclopropyl; R² is selectedfrom halogen, --S(O)_(p) Me and trifluoromethyl, n is two or three; p iszero, one or two; and R³ is C₁₋₄ alkyl; and (b)N-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide)having the formula (II): ##STR5## wherein the weight ratio of (a):(b) isfrom about 1:2000 to 50:1.
 2. The method according to claim 1 whereinthe 4-benzoylisoxazole derivative of formula I is5-cyclopropyl-4-(2-methylsulphonyl-4-trifluoromethyl)benzoylisozaxole.3. The method according to claim 1 using an application rate of from 5to 500 g per hectare of 4-benzoylisoxazole and from 10 to 10,000 g perhectare ofN-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide).4. The method according to claim 1 wherein the locus is used, or to beused, for the growing of a crop.
 5. The method according to claim 4wherein the crop is maize.
 6. The method according to claim 1 using anapplication rate of from about 5 to 200 g per hectare of4-benzoylisoxazole and from about 50 to 5,000 g per hectare ofN-isopropyl-(5-trifiuoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide).7. The method according to claim 6 using an application rate of fromabout 50 to 130 g per hectare of 4-benzoylisoxazole and from about 80 to875 g per hectare ofN-isopropyl-(5-triuoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide).8. The method according to claim 7 using an application rate of fromabout 75 to 100 g per hectare of 4-benzoylisoxazole and from about 300to 500 g per hectare ofN-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide).9. The method according to claim 1 by pre-emergence application.
 10. Aherbicidal composition comprising a synergistic herbicidally effectiveamount of:(a) a 4-benzoylisoxazole derivative of formula I as defined inclaim 1; and (b)N-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide);wherein the weight ratio of (a):(b) is from about 1:2000 to 50:1; inassociation with a herbicidally acceptable diluent or carrier, a surfaceactive agent; or a combination thereof.
 11. The composition according toclaim 10 wherein the 4-benzoylisoxazole derivative of formula I is5-cyclopropyl-4-(2-methylsulphonyl-4-trifluoromethyl)benzoylisozaxole.12. The composition according to claim 10 in which the weight ratio of(a):(b) is from about 1:1000 to 4:1.
 13. The composition according toclaim 12 in which the weight ratio of (a): (b) is from about 1:17.5 to1.63:1.
 14. The composition according to claim 13 in which the weightratio of (a):(b) is from about 1:6.67 to 1:3.
 15. The compositionaccording to claim 10 in the form of a water dispersible granule.
 16. Acombination comprising a synergistic herbicidally effective amountof:(a) a 4-benzoylisozaxole of formula I as defined in claim 1; and (b)N-isopropyl-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-4-(4'-fluoro-oxyacetanilide);wherein the weight ratio of (a):(b) is from about 1:2000 to 50:1.